The present invention relates to vehicle transmissions, especially with automatic gear shifting, and more particularly to a device for preventing a certain order of the engagement/disengagement of tooth clutches.
The conventional stepped transmission for rear-wheel drive vehicles can be regarded as a robust, compact and cost-effective product. A typical example of such a lay-out is shown in FIG. 2 in DE10242823A1. An input shaft is coaxial with a main (output) shaft and parallel with a countershaft. A gearwheel that is rotationally fixed on the input shaft meshes with a gearwheel that is rotationally fixed on the countershaft. Several pairs of meshing gearwheels are then located side by side. In each of these pairs, one gearwheel is coaxial with the countershaft; the other is coaxial with the main shaft. One of these gearwheels is rotationally fixed on its coaxial shaft. The other gearwheel, the loose gearwheel, is free to rotate relative to its coaxial shaft, but can be rotationally locked to the shaft by a mechanical tooth clutch. This construction is used for manually shifted transmissions as well as for automated mechanically engaged transmissions, AMTs. Because of the mechanical tooth clutches, there will during the shift be an intemiption of the power transfer between the engine and the driven wheels of the vehicle. Thus, this type of transmission is not power-shifting.
If the loose gearwheels in two gearwheel pairs at the same time would be locked rotationally to their shafts, the transmission would be blocked and the shafts therein could not rotate. This could lead to damage, e.g., broken gear or clutch teeth, and must be prevented. In manual transmissions, the dominant “H-type” shift pattern enables straightforward design of the shift control system to prevent blocked shafts. In AMTs, blocked shafts can be prevented by proper software, at least under normal conditions. However, in case of faults, e.g., on sensors and/or valves, blocking of shafts could possibly occur. In some designs, this is prevented by designing the automatic shift actuation system similar to a manual one, with one actuator corresponding to longitudinal motion of the shift lever and one actuator corresponding to sideways motion. Such a design might in addition reduce the number of components, but is, in general, not able to allow as quick shifts as a system with one actuator for each tooth clutch. In order to prevent blocked shafts, those latter systems often have an interlocking pin between grooves in the shift actuation parts of two tooth clutches. The length of this pin is adapted to allow one tooth clutch, but not both, engaged. This is a simple, robust and cost-effective design.
Dual clutch transmissions are an interesting crossbreed between power-shifting planetary transmissions and conventional stepped transmissions with power interruption at gear shifts. In principle, a dual clutch transmission has two input shafts, each connectable with a friction clutch to the output shaft of the engine. Functionally, this is equivalent to having two conventional transmissions in parallel and using one at a time for power transfer. The parallel transmission that is not used, idling, for the time being, can have a gear engaged and prepared for a subsequent shift. This shift is carried out by simultaneously disengaging the friction clutch of the previously used parallel transmission and engaging the friction clutch of the previously idling parallel transmission.
When properly designed, dual clutch transmissions have a potential of providing power-shifts at a reasonable production cost and low power losses. This is due to the fact that the rotating parts, i.e., gearwheels, shafts and tooth clutches, are similar to those in conventional stepped transmissions. This, furthermore, enables the use of the same production equipment. So, it makes sense to produce dual clutch transmissions in the same facilities as used for conventional stepped transmissions.
Dual clutch transmissions for rear wheel drive vehicles often have two separate countershafts, one connected to each input shaft. One example is found in U.S. Pat. No. 5,150,628. These countershafts make the transmission considerably wider than a conventional stepped transmission. That may lead to difficulties in installing the transmission into the vehicle. However, in some dual clutch transmission designs there is only one countershaft, e.g., as in DE923402, DE3131156A1 and DE102005044068A1. On this countershaft there are loose gearwheels arranged that can be rotationally connected to each other and to the countershaft by means of mechanical tooth clutches. In a way, this can be regarded as if the second countershaft is arranged coaxial to the first one. The result will be a power-shiftable dual clutch transmission that is not wider than a corresponding conventional stepped transmission. However, the tooth clutches on the countershaft make it more difficult to prevent blocking of shafts. Often, some combinations of the states of three or four tooth clutches may give blocked shafts, whereas other combinations are used for ordinary power transfer. Similar conditions can be found also for dual clutch transmissions that have two separate countershafts. An effective way to prevent blocked shafts in such complex transmissions is to use shift barrels for controlling the tooth clutches, e.g., as in U.S. Pat. No. 5,966,989. Unfortunately, shift barrels normally only allow sequential shifting, i.e., from one gear to the adjacent higher or lower. Multi-step shifts are not possible, in general. Another alternative is to use an active shift blocking system, e.g., as in U.S.RE. 39,598E. That would, however, increase the complexity and cost significantly. For preventing blocked shafts, mechanical systems that involve more than two tooth clutches tend to be complex, cf. US2006/0230861A1, especially if the tooth clutches are arranged on different shafts.
US2009139355 discloses a dual clutch transmission with means for blocking gear changes. The transmission may include: a control bar including a hole; a first shift rail and a second shift rail that are respectively disposed along the control bar; first springs biasing the first rail and the second rail respectively; a first stop and a second stop that are mounted in respective inner grooves of the first rail and the second rail; second springs that elastically support the stops and insert the stops into the hole according to the movement of the rails. Spring loaded stops will engage with one of the shift forks in a predetermined fork position in order to prevent an undesired gear shift. However, these means only prevent undesirable states of two tooth clutches that would give blocking of shafts.
DE 8122318 U1 discloses an interlocking device (FIG. 1-3) arranged to prevent forbidden order of engagement/disengagement of two tooth clutches in a vehicle transmission, where each tooth clutch when in engaged position is arranged to rotationally lock a first shaft to a gearwheel or to a second shaft and when in a disengaged position to rotationally unlock said first shaft from said gearwheel or said second shaft, where for each tooth clutch a shift rod (1, 2) is arranged to push said tooth clutch between an engaged and disengaged position, and where said interlocking device comprises:                a groove (7) arranged in a first (1) of said shift rods, and a second and a third groove (7, 8) arranged in a second (2) of said shift rods,        an interlocking element (10) arranged coplanar with said shift rods, and directed and movable towards said shift rods;        
and where length of said interlocking element is adapted to allow certain combinations and order of engagement/disengagement of said tooth clutches.
It is desirable to further develop an interlocking device for tooth clutches in a vehicle transmission.
It is desirable to provide a simple, reliable and cost-effective mechanical device to only allow engagement/disengagement of two different tooth clutches in a certain order.
According to a first aspect of the invention, there is provided an interlocking device arranged to prevent forbidden order of engagement/disengagement of two tooth clutches in a vehicle transmission, where each tooth clutch when in engaged position is arranged to rotationally lock a first shaft to a gearwheel or to a second shaft and when in a disengaged position to rotationally unlock said first shaft from said gearwheel or said second shaft, where for each tooth clutch a shift rod is arranged to push said tooth clutch between an engaged and disengaged position. The interlocking device comprises:                a groove arranged in a first of said shift rods, and a second and a third groove arranged in a second of said shift rods,        an interlocking element arranged coplanar with said shift rods, and directed and movable towards said shift rods;and where length of said interlocking element is adapted to allow certain combinations and order of engagement/disengagement of said tooth clutches. The device is characterized in that an element partitions said second and third groove and where said element is movably arranged in a hole in said second shift rod such that the interlocking element can push the element down in said hole, allowing the second shift rod to be displaced only one-way when the first shift rod is in an engaged position.        
Said device acts between two tooth clutches, only.
Thereby, a cost-efficient compromise between mechanical complexity and shaft-blocking prevention can be achieved. Said device does not prevent the transmission from being used in a normal way.
According to one embodiment of the invention said hole is slanted.
According to another embodiment of the invention said element is a piston slidably arranged in said slanted hole.
According to a further embodiment of the invention said hole is straight and perpendicular to said shift rods.
According to another embodiment of the invention said element is hinged to said second shift rod by a hinge.
According to a further embodiment of the invention said element is of a lid-like design.
According to another embodiment of the invention said element is pushed towards said grooves by a spring element.
According to a further embodiment of the invention said interlocking element is an interlocking pin.